When asked by New Zealand Transport Agency lawyer Andrew Cameron whether plans for the $90 million project would ease the prospect of urban blight Lee said the flyover would likely be the ''cause of blight'' rather than a remedy to it.

He said there were mitigating factors, "but I'm not sure they would change the shadow, noise and perceived barrier effect'' of the proposed two-lane highway flyover 20m north of the Basin Reserve.

In the US many cities were tearing down elevated freeways because of the urban decay they caused in surrounding neighbourhoods.

Lee cited the example of San Francisco's waterfront Embacadero Freeway, built in 1959 and torn down in 1991 after it was damaged in the 1989 Loma Prieta earthquake.

Following its demolition the surrounding area flourished as a shopping boulevard was built, house prices went up and jobs were created in the area.

Lee also said NZTA modelling was not nearly detailed enough to accurately predict the effect of the flyover because it did not focus closely enough on road, public transport and walking and cycling networks.

''It's less robust and accurate compared to a state of the art model.''

Lee also refuted the claim that traffic around the Basin would only get worse citing research showing across the US, New Zealand driving had been declining for a decade - a trend that started before the global financial crisis, peaking in the mid-2000s.

Young people were driving less because they preferred city-living while baby boomers were cutting back as they entered retirement.Petrol prices, car ownership and parking costs were all rising, which was another reason people were driving less.

Although elevated highways separated traffic flows he said they left a huge impact footprint and shadow.